Radio communication systems are known to comprise one or more base sites that respectively support radio communications for a plurality of communication units. Depending on the type of system (e.g., cellular, trunked two-way, or paging), the communication units might comprise mobile or portable radiotelephones, mobile or portable two-way radios, or selective call receivers (i.e., pagers). In a two-way communication system, each communication unit that desires to communicated registers in the communication system and is assigned to a base site. The base site informs each of the communication units in its coverage area of system conditions (e.g., channel availability, channel allocation, system authorization, etc.) by transmitting system information in a system control signal. In a paging system, registration is assumed and the base site similarly transmits system information to the pagers in its coverage area via a system control signal.
Communication units, such as cellular telephones, typically include a display for visually displaying information (e.g., a telephone number, received signal strength, etc.) to a user of the communication unit. In addition, some communication units also display chronological information to their users. Display of the chronological information permits the user to obtain the current time and date from the communication unit when the communication unit is powered on and operable. To generate the chronological information, the communication units typically contain a dedicated electronic clock circuit. The clock circuit generally includes an oscillator, an integrated circuit (IC) having a memory device and a counter, and a battery for providing direct current (DC) power to the integrated circuit and the oscillator. The dedicated integrated circuit and oscillator together generate and maintain the chronological information in the communication unit. However, the dedicated integrated circuit, oscillator, and battery are independent of the power source and other integrated circuits used for primary operation (e.g., transmission, reception, and control) of the communication unit. Consequently, the dedicated components used to produce the chronological information increase the cost, size, and weight of the communication unit.
As is also known in the art, some communication units and base sites are equipped with satellite receivers to receive chronological information periodically broadcast from global positioning satellites. However, similar to the dedicated components discussed above, the inclusion of such a satellite receiver in a communication unit increases the cost, size, weight and complexity of the communication unit.
Therefore, a need exists for a method and apparatus for providing chronological information to a communication unit in a radio communication system that facilitates the use of the chronological information by a user of the communication unit, without requiring additional electronic hardware to generate, or receive, the chronological information as in prior art radio communication units.